An armed student entered a Moscow school today and took more than 20 teenagers hostage in an incident that also claimed the lives of a policeman and a teacher.

The hostage-taker was one of the students of school number 263 on the northern outskirts of Moscow, police officials said.

A policeman and a biology teacher were killed in the attack.

It came as Russia is on a heightened state of alert before the Winter Olympics opens in Sochi this week.

The gunman held more than 20 teenage biology students and the teacher hostage for about 30 minutes before police moved in.

School official Avitara Sharafetdinova told state television that all children and teachers had been evacuated from the school after the incident.

State television said the student had made no demands and conducted no negotiation with the police before being "neutralised".

A later report said he was detained.